The present invention relates to the art of paper-making and more particularly to a system capable of sensing formation and/or roughness of a paper web during production.
In the past, the examination of paper or paperboard webs during production for sensing roughness has been primarily through the use of mechanical devices such as by means of a stylus riding on the surface of the web to sense the surface roughness. Optical systems have also been used for determining formation but for the most part not on-line with the moving web. Rather, web samples have been taken from the production line and examined off-line, typically by sensing light transmitted through the sample from the interior of a mounting drum which is rotated.
An example of a prior art optical system for use in examining a moving paper web during production for defects including holes and wrinkles in the web is found in U.S. Pat. No. 4,160,913 entitled "WEB SCANNING APPARATUS" which issued on July 10, 1979 to the present applicant. In the disclosed system of U.S. Pat. No. 4,160,913 a flying spot is employed to scan the web for determining the two edges and defects, including holes and wrinkles, in the web. A detector senses the changes in reflected illumination, and a circuit discriminates between a dark signal which yields a positive then negative going pulse to indicate a hole, and a light signal which yields a negative then positive going pulse to indicate a wrinkle. While this prior system is very useful in detecting holes and wrinkles, it is important in the manufacture of paper to provide detecting means for the on-line scanning operation determination of roughness and formation of the paper web.
Accordingly, the present invention is directed to providing an improved optical system for paper testing, either on-line or in a laboratory, which can accurately measure the formation and roughness of paper webs.
It is a further object of the present invention to provide a process and apparatus for measuring formation and roughness of a paper web while on-line irrespective of web velocity and optical source energy variations during the testing operation.